1. Field of the Invention
The invention relates to a clutch device having a flywheel. More specifically, the present invention relates to a clutch device, in which the flywheel has a friction surface to facilitate clutch coupling to a frictional coupling portion of a clutch disk assembly.
2. Background Information
Conventionally, a flywheel is attached to a crankshaft of an engine for absorbing vibrations caused by variations in engine combustion. Further, a clutch device is arranged on a transmission side (i.e., in a position axially shifted toward the transmission) with respect to the flywheel. The clutch device usually includes a clutch disk assembly coupled to an input shaft of the transmission and a clutch cover assembly for biasing the frictional coupling portion of the clutch disk assembly toward the flywheel. The clutch disk assembly typically has a damper mechanism for absorbing and damping torsional vibrations. The damper mechanism has elastic members such as coil springs arranged for compression in a rotating direction.
A structure is also known in which the damper mechanism is not arranged in the clutch disk assembly, and rather is arranged between the flywheel and the crankshaft. In this structure, the flywheel is located on the output side of a vibrating system, in which the coil springs form a border between the output and input sides, so that an inertia on the output side is larger than that in other prior art. Consequently, the resonance rotation speed can be lower than an idling rotation speed so that damping performance is improved. The structure, in which the flywheel and the damper mechanism are combined as described above, provides a flywheel assembly and/or a flywheel damper.
In the flywheel assembly, an disk-like plate called “a flexible plate” is used to connect the flywheel to the crankshaft so that it is possible to decrease bending vibrations from the crankshaft. The flexible plate has a high rigidity in the rotating direction to transmit torque, but it has a low rigidity in the bending direction to deflect or bend in response to the bending vibrations, as shown in Unexamined Japanese Patent Publication H10-231897. When the engine is started or stopped, the rotational speed passes through a resonance point of bending vibration in a low speed range (for example, below 500 rpm). At this time, the bending vibrations become large so that the flexible plate is damaged or sound and vibration become violent.